Lack of effect of sumatriptan and UK-14,304 on capsaicin-induced relaxation of guinea-pig isolated basilar artery

mRNA expression of 5-hydroxytryptamine 1B, 1D, and 1F receptors and their role in controlling the release of calcitonin gene-related peptide in the rat trigeminovascular system

Triptans, a family of 5-hydroxytryptamine (5-HT) 1B, 1D, and 1F receptor agonists, are used in the acute treatment of migraine attacks. The site of action and subtypes of the 5-HT(1) receptor that mediate the antimigraine effect have still to be identified. This study investigated the mRNA expression of these receptors and the role of 5-HT(1) receptor subtypes in controlling the release of calcitonin gene-related peptide (CGRP) in rat dura mater, trigeminal ganglion (TG), and trigeminal nucleus caudalis (TNC). The mRNA for each receptor subtype was quantified by quantitative real-time polymerase chain reaction. A high potassium concentration was used to release CGRP from dura mater, isolated TG, and TNC in vitro. The immunoreactive CGRP (iCGRP) release was measured by enzyme-linked immunoassay. The mRNA transcripts of the 3 5-HT(1) receptor subtypes were detected in the trigeminovascular system. Sumatriptan inhibited iCGRP release by 31% in dura mater, 44% in TG, and 56% in TNC. This effect was reversed by a 5-HT(1B/1D) antagonist (GR127395). The 5-HT(1F) agonist (LY-344864) was effective in the dura mater (26% iCGRP inhibition), and the 5-HT(1D) agonist (PNU-142633) had a significant effect in the TNC (48%), whereas the 5-HT(1B) agonist (CP-94253) was unable to reduce the iCGRP release in all tissues studied. We found that sumatriptan reduced the iCGRP release via activation of 5-HT(1D) and 5-HT(1F) receptor subtypes. The 5-HT(1F) receptor agonist was effective only in peripheral terminals in dura mater, whereas the 5-HT(1D) agonist had a preferential effect on central terminals in the TNC.

Neurovascular pharmacology of migraine

Migraine is a paroxysmal neurovascular disorder, which affects a significant proportion of the population. Since dilation of cranial blood vessels is likely to be responsible for the headache experienced in migraine, many experimental models for the study of migraine have focussed on this feature. The current review discusses a model that is based on the constriction of carotid arteriovenous anastomoses in anaesthetized pigs, which has during the last decades proven of great value in identifying potential antimigraine drugs acting via a vascular mechanism. Further, the use of human isolated blood vessels in migraine research is discussed. Thirdly, we describe an integrated neurovascular model, where dural vasodilatation in response to trigeminal perivascular nerve stimulation can be studied. Such a model not only allows an in-depth characterization of directly vascularly acting drugs, but also of drugs that are supposed to act via inhibition of vasodilator responses to endogenous neuropeptides, or of drugs that inhibit the release of these neuropeptides. We discuss the use of this model in a study on the influence of female sex hormones on migraine. Finally, the implementation of this model in mice is considered. Such a murine model allows the use of genetically modified animals, which will lead to a better understanding of the ion channel mutations that are found in migraine patients.

Experimental migraine models and their relevance in migraine therapy

Although the understanding of migraine pathophysiology is incomplete, it is now well accepted that this neurovascular syndrome is mainly due to a cranial vasodilation with activation of the trigeminal system. Several experimental migraine models, based on vascular and neuronal involvement, have been developed. Obviously, the migraine models do not entail all facets of this clinically heterogeneous disorder, but their contribution at several levels (molecular, in vitro, in vivo) has been crucial in the development of novel antimigraine drugs and in the understanding of migraine pathophysiology. One important vascular in vivo model, based on an assumption that migraine headache involves cranial vasodilation, determines porcine arteriovenous anastomotic blood flow. Other models utilize electrical stimulation of the trigeminal ganglion/nerve to study neurogenic dural inflammation, while the superior sagittal sinus stimulation model takes into account the transmission of trigeminal nociceptive input in the brainstem. More recently, the introduction of integrated models, namely electrical stimulation of the trigeminal ganglion or systemic administration of capsaicin, allows studying the activation of the trigeminal system and its effect on the cranial vasculature. Studies using in vitro models have contributed enormously during the preclinical stage to characterizing the receptors in cranial blood vessels and to studying the effects of several putative antimigraine agents. The aforementioned migraine models have advantages as well as some limitations. The present review is devoted to discussing various migraine models and their relevance to antimigraine therapy.

Lack of effect of the adenosine A1 receptor agonist, GR79236, on capsaicin-induced CGRP release in anaesthetized pigs

Migraine is a common neurological disorder that is associated with an increase in plasma calcitonin gene-related peptide (CGRP) levels. CGRP, a potent vasodilator released from the activated trigeminal sensory nerves, dilates intracranial blood vessels and transmits vascular nociception. Hence, inhibition of trigeminal CGRP release may prevent neurotransmission and, thereby, ameliorate migraine headache. Therefore, the present study in anaesthetized pigs investigates the effects of a selective adenosine A(1) receptor agonist, GR79236 (3, 10 and 30 microg/kg, i.v.) on capsaicin-induced carotid haemodynamic changes and on plasma CGRP release. Intracarotid (i.c.) infusion of capsaicin (10 microg/kg/min, i.c.) increased the total carotid blood flow and conductance as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. These responses to capsaicin were dose-dependently attenuated by GR79236. However, the increases in the plasma CGRP concentrations by capsaicin remained essentially unmodified after GR79236 treatment. The above results suggest that GR79236 may have an antimigraine potential due to its postjunctional effects (carotid vasoconstriction) rather than to prejunctional inhibition of trigeminal CGRP release.

Effects of sumatriptan on capsaicin-induced carotid haemodynamic changes and CGRP release in anaesthetized pigs

It is suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene related peptide (CGRP), resulting in cranial vasodilatation and central nociception. Hence, inhibition of trigeminal CGRP release may prevent the above vasodilatation and, accordingly, abort migraine headache. Therefore, this study investigated the effects of sumatriptan (100 and 300 microg/kg, i.v.) on capsaicin-induced carotid haemodynamic changes and on CGRP release. Intracarotid (i.c.) infusions of capsaicin (10 microg/kg/min, i.c.) increased total carotid, arteriovenous anastomotic and capillary conductances as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. Except for some attenuation of arteriovenous anastomotic changes, the capsaicin-induced responses were not affected by sumatriptan. Moreover, i.c. infusions of capsaicin (0.3, 1, 3 and 10 microg/kg/min, i.c.) dose-dependently increased the jugular venous plasma concentrations of CGRP, which also remained unaffected by sumatriptan. The above results support the contention that the therapeutic action of sumatriptan is mainly due to cranial vasoconstriction rather than trigeminal (CGRP release) inhibition.

Effects of the CGRP receptor antagonist BIBN4096BS on capsaicin-induced carotid haemodynamic changes in anaesthetised pigs

1. Calcitonin gene-related peptide (CGRP), a potent vasodilator released from capsaicin-sensitive trigeminal sensory nerves, seems to be involved in the pathogenesis of migraine. Hence, CGRP receptor antagonists may serve as a novel treatment for migraine. This study was therefore designed to investigate the effects of BIBN4096BS (100, 300 and 1000 microg kg-1, i.v.), a potent and selective CGRP receptor antagonist, on capsaicin-induced carotid haemodynamic changes in anaesthetised pigs. Both vagosympathetic trunks were cut and phenylephrine was infused into the carotid artery (i.c.) to support carotid vascular tone. 2. Infusions of capsaicin (0.3, 1, 3 and 10 microg kg-1 min-1, i.c.) did not alter the heart rate, but dose-dependently increased the mean arterial blood pressure. This moderate hypertensive effect was not modified by BIBN4096BS. 3. Capsaicin infusion (10 microg kg-1 min-1, i.c.) increased total carotid, arteriovenous anastomotic and tissue blood flows and conductances as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. These responses to capsaicin were dose-dependently blocked by BIBN4096BS. 4. Capsaicin infusion (10 microg kg-1 min-1, i.c.) more than doubled the jugular venous plasma concentration of CGRP. This effect was not blocked, but rather increased, by BIBN4096BS. 5. The above results show that BIBN4096BS behaves as a potent antagonist of capsaicin-induced carotid haemodynamic changes that are mediated via the release of CGRP. Therefore, this compound may prove effective in the treatment of migraine.

Inhibitory effect of telmisartan on the blood pressure response to angiotensin II challenge

Telmisartan is a new angiotensin receptor antagonist possessing potent, selective, and insurmountable inhibitory activity specific to the angiotensin II type 1 (AT 1 ) receptor. The current study was performed to determine the inhibition of the angiotensin II pressor response by telmisartan in 48 healthy volunteers challenged with hypertension-inducing doses of i.v. angiotensin II. Subjects were challenged with this dose of angiotensin II at intervals between 0.25 and 48 h after double-blind single-dose oral administration of telmisartan 20 mg (n = 12), 40 mg (n = 12), or 80 mg (n = 12) or placebo (n = 12) in parallel groups. Diastolic and systolic blood pressure and pulse rate were recorded continuously using a servophotoplethysmograph. Urine samples were collected during the study for urinalysis. Tolerability of telmisartan, in comparison with placebo, was also monitored throughout the study. Telmisartan 20-80 mg dose dependently inhibited the increase in diastolic and systolic blood pressure induced by angiotensin II. Telmisartan 40 mg produced 80.1% maximum inhibition, and with 80 mg 89.6% maximum inhibition of diastolic blood pressure was achieved. Inhibition was apparent after 0.3-1.1 h and was still observed 48 h after administration for all telmisartan doses. The inhibitory effect of telmisartan 20, 40, and 80 mg, 48 h after dosing was significantly greater than that of placebo. A > 25% inhibition of the angiotensin II response on diastolic blood pressure was detected until 26.9, 35.4, and 40.5 h, respectively, after telmisartan 20 mg, 40 mg, and 80 mg. Anti-clockwise hysteresis was observed, indicating a delay and longer persistence of effect than to be expected from the plasma concentration-time course. The slow dissociation of telmisartan from the receptor probably contributed to this hysteresis. The incidence of adverse events was comparable in telmisartan-and placebo-treated subjects and was not dose dependent. In conclusion, telmisartan 40 mg provides rapid-onset, well-tolerated, and near-maximal inhibition of angiotensin II-induced hypertension, with maintenance of the inhibitory effect for 48 h.

Effects of telmisartan, hydrochlorothiazide and their combination on blood pressure and renal excretory parameters in spontaneously hypertensive rats

The effects of telmisartan and hydrochlorothiazide (HCTZ) alone and in combination on blood pressure (BP) and renal excretory function were investigated in male spontaneously hypertensive rats (SHR) after oral administration for five consecutive days. Four treatments were studied: vehicle (0.5% Natrosol), telmisartan 3 mg/kg, HCTZ 10 mg/kg, and telmisartan 3 mg/kg+HCTZ 10 mg/kg. The effects on BP and heart rate were studied in 40 SHRs (10 animals per group) using an implanted telemetry device. Renal excretory function was assessed in 76 SHRs (18 animals per group, of which nine were used for urine sampling and nine for blood sampling). The telmisartan/HCTZ combination produced the greatest reductions in trough DBP (-44+/-1.5 mmHg), SBP (-60+/-1.9 mmHg) and mean BP (mBP; -53+/-1.7 mmHg) after five days of therapy (p<0.05 vs. vehicle and vs. telmisartan). Telmisartan monotherapy also decreased DBP, SBP and mBP significantly (p<0.05), but only minor BP fluctuations occurred in SHRs receiving HCTZ or vehicle. Telmisartan/HCTZ elevated heart rate by approximately 12 beats per minute (p<0.05 vs.control). Significant increases in urine volume and Na+, Cl, K+, creatinine and glucose excretion were observed with HCTZ treatment (p<0.01). Telmisartan/HCTZ also promoted renal water and electrolyte excretion (p<0.01); the diuretic effect appeared to be greater with the combination than with HCTZ alone, and there was some attenuation of urinary K+ loss. Elevated blood urea nitrogen levels were observed only in HCTZ-treated SHRs. These results indicate that the antihypertensive efficacy of telmisartan in SHRs is augmented by co-administration with HCTZ. The combination did not affect renal excretory function, with the exception of an increase in blood urea nitrogen and a possible amelioration of HCTZ-related K+ depletion.

Pharmacological evidence for CGRP uptake into perivascular capsaicin sensitive nerve terminals

Specific mechanisms, providing reuptake of cathecholamine and amino acid neurotransmitters (e.g. serotonin and glutamate) into cells of the central nervous system are well known, whereas neuronal uptake of neuropeptide transmitters have not previously been reported. In the present study we present evidence for uptake of the 37 amino acid neuropeptide, calcitonin gene-related peptide (CGRP) into perivascular terminals of capsaicin sensitive nerve fibres, innervating the guinea-pig basilar artery. Release of CGRP from perivascular nerve terminals was obtained by capsaicin-induced vanilloid receptor-stimulation and detected as CGRP receptor-mediated dilation of isolated segments of the guinea-pig basilar artery. Following three repeated capsaicin challenges, CGRP-depleted segments were incubated with CGRP. This caused significant reappearance of capsaicin-induced vasodilatory responses. These responses were dependent on duration and concentration of the preceding CGRP incubation and were inhibited by the CGRP receptor antagonist, CGRP(8 - 37). The CGRP-re-depletion was significantly reduced when CGRP(8 - 37) was present during the preceding CGRP incubation. Thus, presynaptic CGRP receptors are likely to be involved in neuronal CGRP uptake. Incubating the artery segments with (125)I-CGRP allowed subsequent detection of capsaicin-induced (125)I-release. Immunohistochemical experiments showed that only terminal CGRP is subject to capsaicin-induced depletion in vitro, whereas CGRP-immunoreactivity endures in the nerve fibres.

Recent insights into the regulation of cerebral circulation

1. Mechanisms that regulate the cerebral circulation have been intensively investigated in recent years. The role of several vasodilator mechanisms has been examined in the cerebral circulation, including nitric oxide (NO), trigeminal peptides and potassium channels, as well as the potent vasoconstrictor endothelin. These mediators appear to play a role in physiological and pathophysiological responses of the cerebral circulation. In the present review, we will focus on some recent developments in each of these areas. 2. Nitric oxide is an important regulator of cerebral vascular tone. Tonic production of NO maintains the cerebral vasculature in a dilated state. NO appears to be an important vasodilator during activation of neurons by excitatory amino acids, somatosensory stimulation and cortical spreading depression. Tonic production of NO appears to be critical in vasodilatation during hypercapnia, although NO may not directly mediate vasodilatation. NO produced by immunological NO-synthase appears to be important in dilatation following exposure to bacterial endotoxin. 3. Calcitonin gene-related peptide (CGRP), released from trigeminal perivascular sensory nerves in the brain, is an extremely potent dilator of brain vessels. CGRP may limit noradrenaline-induced constriction of cerebral vessels and contribute to dilatation during hypotension (autoregulation), reactive hyperaemia, seizures and cortical spreading depression. 4. Activation of potassium channels leads to hyperpolarization of cerebral vascular smooth muscle and appears to be a major mechanism for dilatation of cerebral arteries. Agents that increase the intracellular concentration of cyclic 3' 5'-adenosine monophosphate (cAMP) produce vasodilatation in part by activation of large conductance calcium-activated potassium channels (BKCa) and ATP-sensitive potassium channels (KATP). Activation of both KATP and BKCa channels also appears to contribute to vasodilatation during hypoxia. In contrast to KATP channels, BKCa channels appears to be active under basal conditions, contributing to tonic dilatation of cerebral blood vessels. 5. Endothelin is produced in the brain, but its role in the physiological regulation of cerebral blood flow is not known. Endothelin may contribute to the spasm of cerebral arteries following subarachnoid haemorrhage.

NK1 and CGRP receptor-mediated dilatation of the carotid arterial bed of the anaesthetized rabbit

The present study has investigated the effects of alpha and beta calcitonin gene-related peptide (CGRP), and the tachykinin neurokinin1 (NK1) receptor agonist, substance P methyl ester (SPOMe), on carotid vascular resistance, following their injection into the carotid artery bed of the anaesthetized rabbit. The involvement of CGRP and NK1 receptors in nicotine-induced alterations in carotid vascular resistance has also been characterized. alpha-or beta CGRP (1 and 10 pmolkg-1 i.a.) and SPOMe (0.01 and 0.1 pmolkg-1 i.a.) caused dose-related increases in carotid arterial blood flow associated with decreases in carotid arterial vascular resistance with little effect on arterial blood pressure. The selective CGRP receptor antagonist, CGRP8-37 (0.34 mumolkg-1 i.v.), caused a rightward displacement of the dose-response curves to both alpha- and beta CGRP; mean dose-ratios, 5 min after antagonist administration, were 14 and 24 respectively. The selective NK1 receptor antagonist, CP99 994 (0.23 mumolkg-1 i.v.), caused a rightward shift in the dose-response curve to SPOMe; mean dose-ratios, 15 and 75 min after antagonist administration, were 42 and 16 respectively. CGRP8-37 (0.34 mumolkg-1) had no effect on decreases in carotid arterial vascular resistance produced by SPOMe, and CP99 994 (0.23 mumolkg-1 i.v.) had no effect on vasodilator responses produced by either alpha- or beta CGRP. Intracarotid injection of nicotine (0.002-2 mumolkg-1) caused dose-dependent transient, followed by a more prolonged, increase in carotid blood flow and reduction in arterial vascular resistance. The prolonged carotid vasodilator response produced by nicotine (0.2 mumolkg-1) was markedly attenuated by CGRP8-37 (0.34 mumolkg-1 i.v.) but unaffected by CP99 994 (1.15 mumolkg-1 i.v.) suggesting a role for CGRP, and not substance P, in this vasodilation. Neither receptor antagonist affected the transient response produced by nicotine. This study has demonstrated that intracarotid injection of NK1 and CGRP receptor agonists to the anaesthetized rabbit results in an increase in carotid blood flow and a reduction in vascular resistance, indicative of vasodilatation of this artery bed. CGRP mediates the nicotine-induced dilatation of the carotid vascular bed, consistent with its release from sensory nerves. This model should prove useful for the in vivo characterization of NK1 or CGRP receptor agonist and antagonist activities, and in the study of neurogenically induced vasodilation.

The modulation of the increase in rat facial skin blood flow observed after trigeminal ganglion stimulation

Electrical stimulation of the trigeminal ganglion causes an increase in facial skin blood flow in the anaesthetised rat, as measured by laser Doppler flowmetry. We investigated the modulation of this neurogenic vasodilator response using selective receptor agonists for putative prejunctional inhibitory receptors, as well as other pharmacological agents to further characterise this response. [D-Ala2,Me-Phe4,Gly5-ol]enkephalin (DAGO, a mu-opioid receptor agonist) inhibited the vasodilator response in a dose-related (0.058-5.8 mumol/kg i.v.) and naloxone-sensitive manner. A similar inhibitory response was observed with the local anaesthetic lignocaine (2% w/v, s.c. 20 microliters). In contrast, the histamine H3-receptor agonist alpha-methylhistamine (15 or 35 mumol/kg, i.v.) and the 5-HT1D receptor agonists sumatriptan (0.24 or 2.4 mumol/kg, i.v.) and CP 122,288 (0.0003-3 mumol/kg, i.v.) had no effect on these responses. Similarly, atropine (1.5 mumol/kg, i.v.) and indomethacin (28 mumol/kg, i.v.) did not alter the vasodilatation observed in this model. In conclusion, only mu-opioid receptor activation and local anaesthetic had any inhibitory action on the neurogenic vasodilatation observed in this model.

Activation of sensory nerves in guinea-pig isolated basilar artery by nicotine: evidence for inhibition of trigeminal sensory neurotransmission by sumatriptan

Nicotine (100 microM), but not electrical field stimulation or potassium chloride (0.1-3 microM), caused capsaicin (1 microM)- and tetrodotoxin (1 microM)-sensitive relaxations of guinea-pig isolated basilar artery precontracted with prostaglandin F2 alpha. Nicotine-induced responses were blocked by the neurokinin NK1 receptor antagonist, GR82334 (10 microM), but were unaffected by the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP-(8-37) (1 microM). This suggests that nicotine activates capsaicin-sensitive sensory nerves in guinea-pig basilar artery to cause relaxation predominantly via substance P release. The vascular 5-HT1 receptor agonist, sumatriptan (0.3 and 3 microM), inhibited nicotine-induced relaxation (by 50 and 80% respectively); the inhibitory effect of sumatriptan (0.3 microM) was attenuated in the presence of the non-selective 5-HT1 receptor antagonist, methiothepin (0.1 microM). These data suggest that sumatriptan can inhibit sensory neurotransmission in guinea-pig basilar artery via activation of inhibitory prejunctional 5-HT1 receptors on sensory nerve terminals.

Sumatriptan. A reappraisal of its pharmacology and therapeutic efficacy in the acute treatment of migraine and cluster headache

Sumatriptan is a potent and selective agonist at a vascular serotonin1 (5-hydroxytryptamine1; 5-HT1) receptor subtype (similar to 5-HT1D) and is used in acute treatment of migraine and cluster headache. Following administration of sumatriptan 100mg orally, relief of migraine headache (at 2 hours) was achieved in 50 to 67% of patients compared with 10 to 31% with placebo in controlled clinical trials. In a comparative study, oral administration of sumatriptan 100mg consistently achieved significantly greater response rates than a fixed combination of ergotamine 2mg plus caffeine 200mg during 3 consecutive migraine attacks (66 vs 48% for first attack). Oral sumatriptan 100mg was also more effective than aspirin 900mg plus metoclopramide 10mg orally in a similar study. In the majority of controlled clinical trials, headache relief (at 1 hour after administration) was achieved in 70 to 80% of patients with migraine receiving sumatriptan 6mg subcutaneously compared with 18 to 26% of placebo recipients. Approximately 40% of patients who initially responded to oral or subcutaneous sumatriptan experienced recurrence of their headache, usually within 24 hours, but the majority of these patients responded well to a further dose of sumatriptan. Patients with cluster headache were treated for acute attacks with sumatriptan 6mg subcutaneously or placebo in 2 crossover trials. Headache relief was achieved within 15 minutes in 74 and 75% of patients receiving sumatriptan in these studies compared with 26 and 35%, respectively, with placebo. Patients receiving sumatriptan 12mg had a similar response rate as those receiving 6mg, but the higher dose was associated with an increased incidence of adverse events. Based on extensive safety data pooled from controlled clinical trials, sumatriptan is generally well tolerated and most adverse events are transient. The most frequently reported adverse events following oral administration include nausea, vomiting, malaise, fatigue and dizziness. Injection site reactions (minor pain and redness of brief duration) occur in approximately 40% of patients receiving subcutaneous sumatriptan, although the incidence appears to be markedly reduced when patients self-administer the drug with an auto-injector. Chest symptoms (mainly tightness and pressure) occur in 3 to 5% of sumatriptan recipients, but have not been associated with myocardial ischaemia except in a few isolated cases. Sumatriptan is contraindicated in patients with ischaemic heart disease, angina pectoris including Prinzmetal (variant) angina, previous myocardial infarction and uncontrolled hypertension, but is not contraindicated in patients with migraine and asthma. Data from long term studies in acute treatment of migraine and cluster headache suggest that sumatriptan remains effective and well tolerated over several months.(ABSTRACT TRUNCATED AT 400 WORDS)

Sumatriptan relaxes isolated porcine ophthalmic artery, but inhibits VIP-induced relaxation

Sumatriptan, a 5-hydroxytryptamine (5HT)1-like receptor agonist, is a new antimigraine drug which is also effective in cluster headache (CH), a disorder with marked ocular circulatory abnormalities. Sumatriptan could putatively exert a therapeutic effect in this vascular bed. The present study is an attempt to assess sumatriptan's vasoactivity in isolated porcine ophthalmic artery (POA) and to verify whether it has similar activity to 5HT, and whether it interferes with the vasodilation induced by calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP). In contrast to 5HT, sumatriptan induced only slight contraction in POA at high concentrations. However, in some artery segments pre-contracted with PGF2 alpha, sumatriptan induced a slight and short-lasting but marked relaxation. In addition, relaxations induced by VIP were inhibited significantly by sumatriptan, whereas CGRP effects were not influenced by the drug. Such reactions suggest that sumatriptan's effect in CH is probably unrelated to direct ocular arterial vasoconstriction.

Neurokinin NK1 receptors mediate plasma protein extravasation in guinea-pig dura

Selective neurokinin receptor agonists and calcitonin gene-related peptide (CGRP) were administered i.v. to anaesthetised guinea-pigs, and plasma protein extravasation was measured in dura and conjunctiva, intra- and extracranial tissues, respectively, innervated by the trigeminal nerve. The neurokinin NK1 receptor agonist, GR73632 enhanced plasma protein extravasation in guinea-pig dura (10 nmol/kg i.v.) and conjunctiva (3 and 10 nmol/kg i.v.). Pretreatment with the neurokinin NK1 receptor antagonist GR82334 (200 nmol/kg i.v.) blocked the response to GR73632 in both tissues. Neurokinin NK2 and NK3 receptor-selective agonists, GR64349 (10 nmol/kg i.v.) and senktide (30 nmol/kg i.v.) respectively, and also the neuropeptide CGRP (10 nmol/kg i.v.) had no significant effect on plasma protein extravasation in intra- or extracranial tissues. We conclude that the neurokinin NK1 receptor mediates plasma protein extravasation in tissues innervated by the trigeminal nerve in guinea-pigs; neurokinin NK2, NK3 and CGRP receptors do not directly mediate extravasation of plasma proteins in these tissues.